1. Field of the Invention
Embodiments of the invention relate to determination of the multiple wireless devices.
2. Background of the Related Art
The determination of the current position of devices or goods plays an increasingly important role in different areas of technology. Examples of such applications are the tracking of parcels on their delivery route or the forwarding of telephone calls depending on the whereabouts of the call recipient. Further examples are known to the person skilled in the art. Known methods for position determination are based on different technical foundations. On the basis of the Global Positioning System (GPS), there are methods for estimating positions which are used in many areas today but are associated with inaccuracies in dense urban environments. The deviations or inaccuracies thus occurring are in the range between 0.1 and 10 m.
Height estimates using GPS receivers are subject to similar limitations of accuracy, whereby position determinations based on the Global Positioning System are too inaccurate in some applications. Moreover, a position determination based on the Global Positioning System requires a line of sight to some of the satellites used, thus frequently making this method unusable within enclosed spaces.
A further method for position determination is based on an analysis of radio cells, for example in the GSM radio network. Mobile telephones according to the GSM standard register with a base station, with the mobile radio network and its operator being informed of the way in which the mobile telephone can be reached. On condition of a sufficient spatial density of such base stations, it is thus possible to a make a position determination of mobile telephones by means of so-called triangulation methods.
In rural areas, however, the density of the base stations is frequently too low for performing such methods. In this respect, walls of buildings also usually have a disruptive effect on the accuracy with which position determinations are possible. Furthermore, the multipath propagation in urban environments, in which the electromagnetic waves are reflected by walls a number of times, makes a position determination in such environments significantly more difficult.
The position determination using wireless networks, such as by means of so-called Wireless Local Area Networks, is subject to similar limitations. In this respect, such networks are predominantly available within buildings or in the vicinity of buildings, and they are subject to similar limitations due to the propagation characteristics of the radio waves used, like the mobile radio networks already mentioned, although they are operated in different frequency ranges.
Radio technologies with even shorter ranges, such as ad hoc radio networks based on the so-called Bluetooth standard, which achieve ranges between a few meters and up to 100 m depending on the class used, in some cases enable fairly accurate estimates of the position, especially if several Bluetooth devices are arranged within the radio range.
Methods for position determination based on ultrasound or infrared radio beacons reach technical limits due to the inability of such waves to penetrate building walls. Within individual rooms, however, such methods provide possibilities for position determination.
Finally, proposals to distribute data to a multitude of radio channels have become known, the intention being to enable the calculation of the distance of a transmitter due to the different arrivals times of the signals. In practice, however, such proposals have not been implemented to date because the radio technology required for this has not yet been developed.